Construction of detention structures has been subject of intensive research due to the need for large quantities of jail space. The requirements of resistance to penetration of the enclosure as well as its need to be fire resistant have generated pre-cast concrete systems as the primary alternative to the standard techniques of formed cast in place concrete, all steel construction or reinforced unit masonry. Reinforced unit masonry is the least resistant to penetration, is subject to joint damage by abrading and is a slow and labor intensive method. Cast in place reinforced concrete can be made acceptably resistant to penetration if heavily reinforced, but is slow due to forming, stripping and curing time requirements, and it is labor intensive, space consuming and very heavy. Pre-cast systems can be built with greater speed than the cast in place concrete but otherwise have the same type of deficiencies, plus they require many special connectors as well as heavy equipment for erection. All steel systems are the most resistant to penetration or damage but are not fire resistant enough for most multi-story structures and are very expensive. The system of this invention overcomes these difficulties by being highly resistant to penetration, lighter weight, fire resistant, easy and fast to erect and highly efficient in use of materials and labor. This invention also provides a joint free cell interior.
Recent tests run on the herein described cementiciously filled light gauge steel structure invention have shown it to be more resistant to penetration than reinforced concrete or reinforced unit masonry. The standard impact test simulates an average man swinging a sixteen pound sledge hammer at one point of the assembly. A six inch thick reinforced concrete wall was penetrated with 1300 blows and an eight inch reinforced unit masonry wall with 800 blows. The light gauge metal sheathed and cementiciously filled wall described in this invention withstood an average of 1982 blows with only minor and easily repairable damage.
Light gauge steel framing used in this invention has been produced by many manufacturers since the late 1940's and is used in both load bearing and non-load bearing construction. It is normally used with finishes on both sides and a hollow or insulated cavity. Diagonal tension strap bracing for horizontal loads is usually screwed or welded to rigid connection points. The straps often are loose or bent during installation and allow damaging movement to occur in the building frame during lateral loading. The bearing wall structures normally built do not provide for continuity of the concrete diaphragm topping unless it is poured separately at each floor level and cured before the next level is erected. When the steel frame is erected with the concrete topping placed after erection in the present art, the continuity of the topping is interrupted at each wall and no continuous diaphragm is possible.
Filled cavity use of light gauge steel framing has been limited to a few systems wherein metal lath is placed on an open truss steel stud frame and the cavity is filled with cement plaster in a multiple pass pneumatic placement operation. Although there is a small composite effect with these methods, the strength of the pneumatically placed cement plaster and metal lath and the composite action are insufficient to appreciably aid in penetration resistance or load capacity of the assembly. The method is very slow, it is not used for multiple story construction, does not adequately provide for lateral forces and is very labor intensive. Several such systems using pneumatic placement of cement have been unsuccessfully marketed for security construction.
A light gauge framing method with reinforced cement finishes was described in U.S. Pat. No. 4,472,919, which relates principally to a method of allowing independent movement of the steel frame and the reinforced cement finish. The method described is not appropriate for penetration resistance in security construction and does not envision any composite action.
Modular building techniques described in U.S. Pat. No. 3,751,864 claim a concrete column and beam type structure created with modular boxes with corrugated steel walls and floor used as permanent forms. This patent limits the modules to one story at a time with structural loads carried by conventionally reinforced columns and beams. Concrete is poured at each story and must cure before the next story of modules is placed. This creates many of the same problems associated with concrete construction in that the concrete placement is subject to weather considerations and all concrete must cure on each floor before the next floor modules can be set. There is no great increase in speed of construction over normal methods and the steel is not acting in a composite way.
A structure of modular units is also described in U.S. Pat. No. 3,678,638 that describes a column and beam structure of concrete formed by the module walls. The steel framing of the modules is not intended to carry any permanent loads and the structure must be erected one story at a time and requires many special parts. Due to the one floor at a time pouring and curing of concrete it will not improve construction speed.